1. A Measurement Study of Peer-to-Peer File Sharing Systems
Stefan Saroiu, P. Krishna Gummadi, Steven D. Gribble
Presented by Zhengxiang Pan
March 18th, 2003

2. Introduction Napster & Gnutella Population of users
Bottleneck bandwidth of hosts & latencies
Duration time of remain connected
Number of files shared & downloaded

3. Methodology-architecture
Napster’s architecture
A cluster of central servers
Each peer connects to one server
Servers cooperate to process query
Gnutella’s architecture
No centralized servers
Peers form overlay network
Send a query by a controlled flood

4. Methodology-crawler Napster crawler Gnutella crawler
A larger number of connections to a single server
Issue popular queries in parallel
Captured 40%-60% local users
Gnutella crawler
Iteratively send ping messages with large TTLs
Discover new hosts by receiving pong messages.
Capture 25%-50% of the total population

5. Methodology-directly measure characteristics
Latency
Measure the time spent by exchanging a 40-byte TCP packet.
Lifetime
Offline: not respond to TCP SYN packets
Inactive: respond with TCP RST
Active: accept the connection
Bottleneck bandwidth
Approximate to available bandwidth
Actively measure upstream and downstream using a few TCP packets

6. Results-bandwidth Downstream & upstream bottleneck bandwidth
-50% in Napster & 60% in Gnutella use broadband connections
-25% in Napster & 8% in Gnutella use modems
-20% in Napster & 30% in Gnutella have high bandwidth (>3Mbps)

7. Result-reported bandwidth
22% in Napster report “unknown” bandwidth

8. Result- latency Latencies for Gnutella users
-Unstructured, ad-hoc, a substantial fraction suffer from high-lantency
-Difference in trans-oceanic peers

9. Result- availability
-only 20% peers had an IP-level uptime of 93% or more
-Median session duration : 60 minutes

10. Result-files -25% in Gnutella do not share any files
-40%-60% peers share 5%-20% of the shared files

11. Result-download & upload
the percentage of peers in each bandwidth class is roughly the same as the percentage of files shared by that bandwidth class.

12. Result- cooperate
-30% of the users that report their bandwidth as 64 Kbps or less actually have a significantly greater bandwidth.
-10% of the users reporting high bandwidth (3Mbps or higher) in reality have significantly lower bandwidth.

13. Result-resilience of Gnutella overlay
Although highly resilient in the face of random breakdowns, Gnutella is nevertheless highly vulnerable in the face of well-orchestrated, targeted attacks.

14. Conclusion Heterogeneity of hosts
Carefully delegate responsibilities
Clearly evidence of client-like and server-like behaviors
Peers tend to misreport information if there is an incentive to do so
Built-in incentive for telling the truth
Verify reported information